posix-timers: Drop redundant memset() invocation

Initially in commit 6891c450 memset() was required to clear a variable
allocated on stack. Commit 2482097c removed the on stack variable and
retained the memset() despite the fact that the memory is allocated via
kmem_cache_zalloc() and therefore zereoed already.

Drop the redundant memset().

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/Z9ctVxwaYOV4A2g4@grain